Date:   Wed, 25 Nov 2020 16:22:46 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Joel Becker <jlbec@...lplan.org>, Christoph Hellwig <hch@....de>
Cc:     linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bgolaszewski@...libre.com>
Subject: [PATCH 3/4] configfs: implement committable items

From: Bartosz Golaszewski <bgolaszewski@...libre.com>

This implements configfs committable items. We mostly follow the
documentation except that we extend config_group_ops with uncommit_item()
callback for reverting the changes made by commit_item().

Each committable group has two sub-directories: pending and live. New
items can only be created in pending/. Attributes can only be modified
while the item is in pending/. Once it's ready to be committed, it must
be moved over to live/ using the rename() system call. This is when the
commit_item() function will be called.

Implementation-wise: we reuse the default group mechanism to elegantly
plug the new pseude-groups into configfs. The pending group inherits the
parent group's operations so that config_items can be seamlesly created
in it using the callbacks supplied by the user as part of the committable
group itself.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@...libre.com>
---
 Documentation/filesystems/configfs.rst |   6 +-
 fs/configfs/configfs_internal.h        |   2 +
 fs/configfs/dir.c                      | 239 ++++++++++++++++++++++++-
 fs/configfs/file.c                     |   8 +
 include/linux/configfs.h               |   1 +
 5 files changed, 247 insertions(+), 9 deletions(-)

diff --git a/Documentation/filesystems/configfs.rst b/Documentation/filesystems/configfs.rst
index 1d3d6f4a82a9..7e0e7c356450 100644
--- a/Documentation/filesystems/configfs.rst
+++ b/Documentation/filesystems/configfs.rst
@@ -290,6 +290,7 @@ config_item_type::
 		struct config_group *(*make_group)(struct config_group *group,
 						   const char *name);
 		int (*commit_item)(struct config_item *item);
+		int (*uncommit_item)(struct config_item *item);
 		void (*disconnect_notify)(struct config_group *group,
 					  struct config_item *item);
 		void (*drop_item)(struct config_group *group,
@@ -490,9 +491,6 @@ pass up an error.
 Committable Items
 =================
 
-Note:
-     Committable items are currently unimplemented.
-
 Some config_items cannot have a valid initial state.  That is, no
 default values can be specified for the item's attributes such that the
 item can do its work.  Userspace must configure one or more attributes,
@@ -532,4 +530,4 @@ method returns zero and the item is moved to the "live" directory.
 As rmdir(2) does not work in the "live" directory, an item must be
 shutdown, or "uncommitted".  Again, this is done via rename(2), this
 time from the "live" directory back to the "pending" one.  The subsystem
-is notified by the ct_group_ops->uncommit_object() method.
+is notified by the ct_group_ops->uncommit_item() method.
diff --git a/fs/configfs/configfs_internal.h b/fs/configfs/configfs_internal.h
index 855f00868654..22b649567b13 100644
--- a/fs/configfs/configfs_internal.h
+++ b/fs/configfs/configfs_internal.h
@@ -56,6 +56,8 @@ struct configfs_dirent {
 #define CONFIGFS_USET_DROPPING		BIT(8)
 #define CONFIGFS_USET_IN_MKDIR		BIT(9)
 #define CONFIGFS_USET_CREATING		BIT(10)
+#define CONFIGFS_GROUP_PENDING		BIT(11)
+#define CONFIGFS_GROUP_LIVE		BIT(12)
 #define CONFIGFS_NOT_PINNED	(CONFIGFS_ITEM_ATTR | CONFIGFS_ITEM_BIN_ATTR)
 
 extern struct mutex configfs_symlink_mutex;
diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index b0983e2a4e2c..73e3bd30a2ad 100644
--- a/fs/configfs/dir.c
+++ b/fs/configfs/dir.c
@@ -655,6 +655,13 @@ static void detach_groups(struct config_group *group)
 
 		inode_unlock(d_inode(child));
 
+		/*
+		 * Free memory allocated for the pending and live directories
+		 * of committable groups.
+		 */
+		if (sd->s_type & (CONFIGFS_GROUP_PENDING | CONFIGFS_GROUP_LIVE))
+			kfree(sd->s_element);
+
 		d_delete(child);
 		dput(child);
 	}
@@ -859,6 +866,133 @@ static void configfs_detach_item(struct config_item *item)
 	configfs_remove_dir(item);
 }
 
+static bool is_committable_group(struct config_item *item)
+{
+	const struct config_item_type *type = item->ci_type;
+
+	if (type && type->ct_group_ops &&
+	    type->ct_group_ops->commit_item &&
+	    type->ct_group_ops->uncommit_item)
+		return true;
+
+	return false;
+}
+
+struct pending_group_data {
+	struct config_group group;
+	struct config_item_type type;
+	struct configfs_group_operations group_ops;
+};
+
+struct live_group_data {
+	struct config_group group;
+	struct config_item_type type;
+};
+
+static int create_pending_group(struct config_item *parent_item,
+				struct configfs_fragment *frag)
+{
+	const struct config_item_type *parent_type = parent_item->ci_type;
+	struct pending_group_data *pending;
+	struct configfs_dirent *sd;
+	int ret;
+
+	pending = kzalloc(sizeof(*pending), GFP_KERNEL);
+	if (!pending)
+		return -ENOMEM;
+
+	/*
+	 * Let's inherit the group_ops from the parent except for item
+	 * committing and uncommitting.
+	 */
+	memcpy(&pending->group_ops, parent_type->ct_group_ops,
+	       sizeof(struct configfs_group_operations));
+	pending->type.ct_group_ops = &pending->group_ops;
+	pending->type.ct_group_ops->commit_item = NULL;
+	pending->type.ct_group_ops->uncommit_item = NULL;
+
+	/* Let's directly reuse item_ops. */
+	pending->type.ct_item_ops = parent_type->ct_item_ops;
+	pending->type.ct_owner = parent_type->ct_owner;
+
+	config_group_init_type_name(&pending->group, "pending", &pending->type);
+
+	ret = create_default_group(to_config_group(parent_item),
+				   &pending->group, frag);
+	if (ret) {
+		kfree(pending);
+		return ret;
+	}
+
+	link_group(to_config_group(parent_item), &pending->group);
+
+	sd = pending->group.cg_item.ci_dentry->d_fsdata;
+	/* Allow creating config_items in 'pending' group. */
+	sd->s_type |= (CONFIGFS_GROUP_PENDING | CONFIGFS_USET_DIR);
+
+	return 0;
+}
+
+static int create_live_group(struct config_item *parent_item,
+			     struct configfs_fragment *frag)
+{
+	struct live_group_data *live;
+	struct configfs_dirent *sd;
+	int ret;
+
+	live = kzalloc(sizeof(*live), GFP_KERNEL);
+	if (!live)
+		return -ENOMEM;
+
+	live->type.ct_owner = parent_item->ci_type->ct_owner;
+
+	config_group_init_type_name(&live->group, "live", &live->type);
+
+	ret = create_default_group(to_config_group(parent_item),
+				   &live->group, frag);
+	if (ret) {
+		kfree(live);
+		return ret;
+	}
+
+	link_group(to_config_group(parent_item), &live->group);
+
+	sd = live->group.cg_item.ci_dentry->d_fsdata;
+	sd->s_type |= CONFIGFS_GROUP_LIVE;
+
+	return 0;
+}
+
+static int create_committable_groups(struct config_item *parent_item,
+				     struct configfs_fragment *frag)
+{
+	struct configfs_dirent *sd;
+	int ret;
+
+	ret = create_pending_group(parent_item, frag);
+	if (ret)
+		return ret;
+
+	ret = create_live_group(parent_item, frag);
+	if (ret) {
+		detach_groups(to_config_group(parent_item));
+		return ret;
+	}
+
+	/* Disallow creating items directly in the committable group. */
+	sd = parent_item->ci_dentry->d_fsdata;
+	sd->s_type &= ~CONFIGFS_USET_DIR;
+
+	return 0;
+}
+
+static void dentry_mark_dead(struct config_item *item, struct dentry *dentry)
+{
+	configfs_detach_item(item);
+	d_inode(dentry)->i_flags |= S_DEAD;
+	dont_mount(dentry);
+}
+
 static int configfs_attach_group(struct config_item *parent_item,
 				 struct config_item *item,
 				 struct dentry *dentry,
@@ -884,11 +1018,15 @@ static int configfs_attach_group(struct config_item *parent_item,
 		inode_lock_nested(d_inode(dentry), I_MUTEX_CHILD);
 		configfs_adjust_dir_dirent_depth_before_populate(sd);
 		ret = populate_groups(to_config_group(item), frag);
-		if (ret) {
-			configfs_detach_item(item);
-			d_inode(dentry)->i_flags |= S_DEAD;
-			dont_mount(dentry);
+		if (ret)
+			dentry_mark_dead(item, dentry);
+
+		if (is_committable_group(item)) {
+			ret = create_committable_groups(item, frag);
+			if (ret)
+				dentry_mark_dead(item, dentry);
 		}
+
 		configfs_adjust_dir_dirent_depth_after_populate(sd);
 		inode_unlock(d_inode(dentry));
 		if (ret)
@@ -1455,7 +1593,7 @@ static int configfs_rmdir(struct inode *dir, struct dentry *dentry)
 	struct config_item *parent_item;
 	struct config_item *item;
 	struct configfs_subsystem *subsys;
-	struct configfs_dirent *sd;
+	struct configfs_dirent *sd, *parent_sd;
 	struct configfs_fragment *frag;
 	struct module *subsys_owner = NULL, *dead_item_owner = NULL;
 	int ret;
@@ -1474,6 +1612,12 @@ static int configfs_rmdir(struct inode *dir, struct dentry *dentry)
 		return -EINVAL;
 	}
 
+	parent_sd = dentry->d_parent->d_fsdata;
+	if (parent_sd->s_type & CONFIGFS_GROUP_LIVE) {
+		config_item_put(parent_item);
+		return -EPERM;
+	}
+
 	/* configfs_mkdir() shouldn't have allowed this */
 	BUG_ON(!subsys->su_group.cg_item.ci_type);
 	subsys_owner = subsys->su_group.cg_item.ci_type->ct_owner;
@@ -1560,9 +1704,94 @@ static int configfs_rmdir(struct inode *dir, struct dentry *dentry)
 	return 0;
 }
 
+static int configfs_rename(struct inode *old_dir, struct dentry *old_dentry,
+			   struct inode *new_dir, struct dentry *new_dentry,
+			   unsigned int flags)
+{
+	struct configfs_dirent *sd, *old_parent_sd, *new_parent_sd;
+	struct dentry *old_parent_dentry, *new_parent_dentry;
+	struct configfs_dirent *committable_group_sd;
+	struct dentry *committable_group_dentry;
+	struct config_item *committable_group_item, *item, *new_parent_item;
+	struct configfs_subsystem *committable_group_subsys;
+	struct configfs_group_operations *committable_group_ops;
+	int ret = 0;
+
+	if (flags)
+		return -EINVAL;
+
+	old_parent_dentry = old_dentry->d_parent;
+	new_parent_dentry = new_dentry->d_parent;
+
+	sd = old_dentry->d_fsdata;
+	old_parent_sd = old_dentry->d_parent->d_fsdata;
+	new_parent_sd = new_dentry->d_parent->d_fsdata;
+
+	if (!old_parent_sd || !new_parent_sd)
+		return -EPERM;
+
+	/*
+	 * Renaming must always be between a 'pending' and a 'live' group and
+	 * both need to have the same parent.
+	 */
+	if (!((old_parent_sd->s_type & CONFIGFS_GROUP_PENDING) &&
+	      (new_parent_sd->s_type & CONFIGFS_GROUP_LIVE)) &&
+	    !((old_parent_sd->s_type & CONFIGFS_GROUP_LIVE) &&
+	      (new_parent_sd->s_type & CONFIGFS_GROUP_PENDING)))
+		return -EPERM;
+
+	if (old_parent_dentry->d_parent != new_parent_dentry->d_parent)
+		return -EPERM;
+
+	committable_group_dentry = old_parent_dentry->d_parent;
+	committable_group_sd = committable_group_dentry->d_fsdata;
+	/*
+	 * Grab a reference to the committable group for the duration of
+	 * this function.
+	 */
+	committable_group_item =
+		configfs_get_config_item(committable_group_dentry);
+	committable_group_subsys =
+		to_config_group(committable_group_item)->cg_subsys;
+	committable_group_ops = committable_group_item->ci_type->ct_group_ops;
+
+	item = sd->s_element;
+	new_parent_item = new_parent_sd->s_element;
+
+	if (WARN_ON(!is_committable_group(committable_group_item))) {
+		/* This would be a result of a programming error in configfs. */
+		config_item_put(committable_group_item);
+		return -EPERM;
+	}
+
+	mutex_lock(&committable_group_subsys->su_mutex);
+	spin_lock(&configfs_dirent_lock);
+
+	if ((old_parent_sd->s_type & CONFIGFS_GROUP_PENDING) &&
+	    (new_parent_sd->s_type & CONFIGFS_GROUP_LIVE))
+		ret = committable_group_ops->commit_item(item);
+	else
+		ret = committable_group_ops->uncommit_item(item);
+	if (ret)
+		goto out;
+
+	new_dentry->d_fsdata = sd;
+	list_move(&sd->s_sibling, &new_parent_sd->s_children);
+	item->ci_parent = new_parent_item;
+	d_move(old_dentry, new_dentry);
+
+out:
+	spin_unlock(&configfs_dirent_lock);
+	mutex_unlock(&committable_group_subsys->su_mutex);
+	config_item_put(committable_group_item);
+
+	return ret;
+}
+
 const struct inode_operations configfs_dir_inode_operations = {
 	.mkdir		= configfs_mkdir,
 	.rmdir		= configfs_rmdir,
+	.rename		= configfs_rename,
 	.symlink	= configfs_symlink,
 	.unlink		= configfs_unlink,
 	.lookup		= configfs_lookup,
diff --git a/fs/configfs/file.c b/fs/configfs/file.c
index 1f0270229d7b..a20e55fd05e8 100644
--- a/fs/configfs/file.c
+++ b/fs/configfs/file.c
@@ -243,9 +243,17 @@ fill_write_buffer(struct configfs_buffer * buffer, const char __user * buf, size
 static int
 flush_write_buffer(struct file *file, struct configfs_buffer *buffer, size_t count)
 {
+	struct config_item *parent_item = buffer->item->ci_parent;
 	struct configfs_fragment *frag = to_frag(file);
+	struct configfs_dirent *sd;
 	int res = -ENOENT;
 
+	if (parent_item && parent_item->ci_dentry) {
+		sd = parent_item->ci_dentry->d_fsdata;
+		if (sd->s_type & CONFIGFS_GROUP_LIVE)
+			return -EPERM;
+	}
+
 	down_read(&frag->frag_sem);
 	if (!frag->frag_dead)
 		res = buffer->attr->store(buffer->item, buffer->page, count);
diff --git a/include/linux/configfs.h b/include/linux/configfs.h
index 4f76dcc08134..ff6b0e408136 100644
--- a/include/linux/configfs.h
+++ b/include/linux/configfs.h
@@ -219,6 +219,7 @@ struct configfs_group_operations {
 	struct config_item *(*make_item)(struct config_group *group, const char *name);
 	struct config_group *(*make_group)(struct config_group *group, const char *name);
 	int (*commit_item)(struct config_item *item);
+	int (*uncommit_item)(struct config_item *item);
 	void (*disconnect_notify)(struct config_group *group, struct config_item *item);
 	void (*drop_item)(struct config_group *group, struct config_item *item);
 };
-- 
2.29.1

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